Calculation and evaluation of the vital head organs dose during Neutron Therapy in Tehran Research Reactor using Zubal phantom

In the recent years some studies has been done to consider the capability of Tehran Research Reactor for Boron neutron capture therapy (BNCT). The purpose of this study is to evaluate the sensitive organs dose during the treatment of patient with deep brain tumor by TRR. The calculation has been carried out using the Monte Carlo code MCNPX for ZUBAL head and neck phantom. The method was tested for 3 different boron concentration injected to patient located in TRR thermal column from human head. The total dose (Dw) was defined as the sum of physical dose components (Di) multiplied by weighting factors (wi) of each dose component in a tissue. The MCNP simulations were carried out with the MCNPX version of 2.6. In order to calculate the dose absorption, the tally F4 was used. For the dose conversion, pointwise KERMA factors from ICRU-46 were directly input with DE and DF cards.
Treatment time based on absorbing 20 Gy-Eq by tumor approximately from 15 to 30 minutes changes for all trials. The results indicate that increasing boron concentration causes decreasing lens and thyroid dose received. In all trials parietal lobes receive the most dese rather than other parts. It was found that fast neutron dose component has most contribution in skin and lenses doses. But for the thyroid gamma dose component has most contribution. It is considered that side-irradiation would not be safe treatment for vital organs and take long time.